Fix handling optimize.enabled from java_defaults

Some module types (`android_test`, etc.) set `optimize.enabled` by
default. If such module happens to have `defaults` attribute which
clears `optimize.enabled`, the latter value is ignored.

Fixes: 129858282
Test: unit tests in java_test.go,
`atest CtsExtendedMockingTestCases` succeeds with aog/936802
reverted (that is, with cts/test/mocking converted to Android.bp)

Change-Id: Ib8e3a0ab0bd489d70ed07f626082aeae31c45e7c